Snow, ice brief update – 830 pm CST

The Arctic cold front has entered north Alabama, with winds turning to NW and temperatures falling quickly into 40s. Deeper into the cold air but not far away, it is 36 in Oxford, MS and 21 in Fayetteville, AR. That air is rushing toward Alabama partially to its own weight, at wind speeds 15-35 mph. The cold front will reach BHM, TCL, and GAD around 11 pm, and temperatures will go below freezing around 6 am.

Radar shows rain along and behind the front. There has been a lot of talk about snow and ice for tomorrow morning’s rush hour in central Alabama. It is difficult for precipitation to survive in an area of cold advection, where cold air is replacing warm air and therefore flows downhill slightly, drying up precipitation. In addition, the cold air will come in shallow,, so there will be a warm nose aloft preventing snow from reaching the ground (see figure).

The problem COULD BE a brief window tomorrow morning where there is still precipitation, likely rain, falling out of it, then reaching the ground and freezing, causing some icy bridges. This is most likely in north Alabama, but is even a possibility as far SE as I-59. Another possibility is that we get 1/2″ of rain overnight, and the cold air comes in so fast some of the water puddles freeze on a few bridges. The thing helping us out on this is the very warm ground temperatures, thanks to sunshine yesterday and BHM reaching 72 degrees today. I don’t see this as a big deal, but you definitely want to check weather in the morning before leaving home, and be careful on bridges and higher elevation roads.

The cold air will be downright crazy! Temperatures will hover between 30 and 35 degrees all day tomorrow in BHM, and with northwest winds 15-30 mph, wind chills will range between 5 and 20 degrees during the day! We will drop slowly through the 20s tomorrow night, ending up near 22 degrees Tuesday morning. We will be below freezing for 24 out of 28 hours from 6 am Tue through 10 am Wed, and 17 hours straight. Remember pets, plants, pipes. And most of all, the elderly or disabled who may not have access to safe, sufficient heat.